I. Field of the Invention
This invention relates to an X-ray diagnostic apparatus for utilizing X-ray digital radiography, and more particularly to an X-ray diagnostic apparatus by which a deterioration on the resolution of X-ray images taken by X-ray TV cameras can be prevented due to a difference existing in the aspect ratios of the employed TV cameras.
II. Description of the Prior Art
FIG. 1 shows a block diagram of the typical conventional X-ray diagnostic apparatus.
Reference numeral 1 denotes an X-ray tube. Pulsed X-rays are exposed toward an object to be examined from the X-ray tube 1 to which a high voltage generated by an extra high tension generating device 2 is applied. Reference numeral 4 indicates an image intensifier which receives an X-ray image penetrating through the object (to which the X-rays are exposed) and then converts the X-ray image into a corresponding optical image. The optical image output from the image intensifier 4 is projected onto a pick-up tube of a TV camera 6 via an optical system/a diaphragm 5, and thereafter is converted into a video signal in a camera control unit 7 (referred to "CCU"). The video signal is supplied to a video processor 8. This video signal is converted into a digital video signal by an analog/digital converter 11 in such a manner that the former signal derived from CCU 7 is supplied to the converter 11 via an input selector 9 and, if necessary, a log amplifier 10. In a normal condition, the video signal from the input selector 9 is directly supplied to the A/D converter 11 via a switch 40 so as to bypass the log amplifier 10. The video signal which has been converted into a digital form is processed in an arithmetic and logic unit 12 (referred to as "ALU") and then stored in a first frame memory 13. This processing operation is a so-called "first arithmetic operation" in this specification. The first arithmetic operation includes the following processing operation. That is, the mask image signals are summed for e.g., several frames and an average thereof is taken so as to eliminate random noises contained in those signals.
It should be noted that the first frame memory 13 stores the digital video signal which is obtained by converting the X-ray image signal that was taken before injection of the X-ray contrast medium into the object 3 ("mask image memory").
Reference numeral 14 denotes a second frame memory 14 whose memory construction is the same as the first frame memory 13. This second frame memory 14 is to store the digital video signal which is obtained by converting the X-ray image signal that was taken after injection of the X-ray contrast medium into the object 3 ("contrast image memory"). This storing process is completely identical to that of the first frame memory 13. Two sets of the digital signals which are stored in the first and second frame memories 13 and 14 are subtraction-processed in ALU 12 as "a second arithmetic operation" to obtain a subtraction video signal. The subtraction video signal is supplied via a video signal enhancement circuit 15 to a digital/analog converter 16. Then it is converted into an analog video signal in the D/A converter 16 so that the subtraction video signal is displayed on a first monitor 17, or recorded by a video disc recorder 18.
The other D/A converter 19 is provided in the video processor 8 so as to convert such a digital video signal that is not yet subtraction-processed into an analog video signal (mask image signal). The analog video signal from the second D/A converter 19 is supplied to a second monitor 20 so as to display the mask image of the object 3. This analog video signal is also supplied, for recording, to a multiformat camera 21.
The video disc recorder 18 has a memory capacity of e.g., 600 TV frames. The output video signal from the video disc recorder 18 is fed out at arbitrary timing into the input selector 9 of the video processor 8, and may be displayed through the video processor 8 on the first monitor 17.
Reference numeral 22 indicates an interface circuit for X-ray diagnostic apparatus and 23 denotes a system control panel of the video processor 8.
In such a conventional X-ray diagnostic apparatus, two types of X-ray TV cameras are generally employed i.e., one for an R/F table system and the other for an angiographing system. Generally speaking, the aspect ratio of the former camera is 1:1, on the other hand that of the latter camera is 3:4. It is, of course designed for the X-ray diagnostic apparatus employing the TV camera of (1:1) aspect ratio that the video processor can process the video signal derived from the above-mentioned TV camera. Similarly the video processor 8 for, the TV camera of (3:4) aspect ratio is designed to be adapted to such an aspect ratio.
Since originally the X-ray diagnostic apparatus is very expensive, it is desirable that one apparatus can utilize TV cameras for not only the R/F table system, but also the angiographing system. In other words, it is expected that two different aspect ratios of TV cameras can be electrically connected to one diagnostic apparatus.
There are however the following problems when the TV camera for the angiographing system (aspect ratio, 3:4) is directly connected to such an X-ray diagnostic apparatus that can be adapted to the TV camera for the R/F table system (aspect ratio, 1:1). That is, because the scanning length of the pick-up tube becomes practically 4/3 times longer than that in the original aspect ratio during one horizontal scanning period, the horizontal resolution is deteriorated by 3/4 times, compared with the use of a TV camera having the aspect ratio (1:1).
It is an object of the present invention to eliminate such conventional problems.
It is further an object of the present invention to provide an X-ray diagnostic apparatus in which deterioration of the horizontal resolution and the contrast variation caused by a difference in the aspect ratios can be prevented by additionally introducing a simple circuit therein.